\documentclass{article}
\usepackage{pgfplots}
\begin{document}
\thispagestyle{empty}
\begin{tikzpicture}
	\begin{axis}
		\addplot {x^2} node [pos=0.75,%
			pin%
			=%
				{%
					-10:$x^2$%
				}%
			,inner sep=0pt] {};
		\addplot {1.5*x^2} node [pos=0.75,%
			pin%
			=%
				{%
					170:$1.5 x^2$%
				}%
			,inner sep=0pt] {};
	\end{axis}
\end{tikzpicture}

\begin{tikzpicture}
	\begin{axis}[
			axis y line=center,
			axis x line=middle,
			axis on top=true,
			xmin=-7,
			xmax=7,
			ymin=-4,
			ymax=4,
			clip=false
		]

		\addplot[
			mark=none,
			domain=-4:6,
			samples=80,
			red,
			thick,
		] {(x<-2)*-2 + (!(x<-2) && (x<3))*x + (!(x<3)) * 3}
		node[pos=0.1,%
			pin%
			=135:%
				{%
					\color{purple}$f(x)=-2$%
				}%
		] {}
		node[pos=0.6,%
			pin%
			=135:%
				{%
					\color{blue}$f(x)=x$%
				}%
		] {}
		node[pos=0.9,%
			pin%
			=135:%
				{%
					\color{green!70!black}$f(x)=3$%
				}%
		] {}
		;
	\end{axis}
\end{tikzpicture}

\end{document}
